Recently, the development of a technology for presenting a stereoscopic video has advanced, and head-mounted displays (hereinafter described as “HMDs”) capable of presenting stereoscopic video having depth have spread. Such HMDs include a shielded HMD that completely covers and shields a field of view of a user wearing the HMD and which can therefore provide a deep sense of immersion to the user observing video. An optical see-through HMD has also been developed as another kind of HMD. The optical see-through HMD is a stereoscopic image device that, using a holographic element, a half-silvered mirror, or the like, can present an augmented reality (AR) image, which is virtual stereoscopic video, to the user, and present a state of a real space outside the HMD to the user in a see-through manner.